Commercial processes associated with the manufacture of semiconductor grade silicon can result in gaseous vent streams which contain hydrogen chloride and hydrosilanes. Both for environmental and economic reasons it is desirable to recover the chloride ion of the hydrogen chloride and to recover the hydrosilanes. The present inventors have found that the recovery of the hydrosilanes and the chloride ion of the hydrogen chloride from the gaseous vent stream can be facilitated by using the hydrogen chloride to chlorinate the hydrosilanes. The process is conducted in the presence of a chlorination catalyst. The present process not only facilitates recovery of the chloride ion of the hydrogen chloride as a substituent of a chlorosilane, but also increases the boiling point of the hydrosilanes by chlorination making them easier to recover by standard processes such as condensation.
Petrov et al., Synthesis of Organosilicon Monomers, Consultants Bureau, N.Y., 1964, p. 416, report that the Si--H bonds of silicon hydrides such as SiH.sub.4, SiH.sub.3 Cl, and CH.sub.3 SiH.sub.3 will react with hydrogen chloride in the presence of AlCl.sub.3 to effect chlorination of the silicon hydride.
Sommer et al., J. Org. Chem. 32:2470-2472 (1967) disclose that organosilicon hydrides react with hydrogen halides in the presence of Group VIII metals to form organosilicon halides and hydrogen.
Bokerman et al., U.S. Pat. No. 4,985,579, issued Jan. 15, 1991, describe a process for the removal of hydrogen containing silane impurities from organosilanes with similar boiling points. In the process described by Bokerman et al., the hydrogen-containing silane is reacted with a hydrogen halide in the presence of a catalyst to replace the hydrogen on the silane with a halide and created a modified silane. The substitution of the heavier halide for the hydrogen increases the boiling point of the modified silane to facilitate the separation of the modified silane from the organosilanes having a similar boiling point.
The cited art does not recognize that in a gaseous vent stream containing hydrogen chloride and hydrosilanes, recovery of the hydrosilanes and the chloride ion of the hydrogen chloride can be facilitated by contacting the gaseous vent gas with a chlorination catalyst. Therefore, it is an objective of the present invention to provide a method for recovery of the hydrogen chloride ion of hydrogen chloride from a vent stream also containing hydrosilanes. Furthermore, it is an objective of the present invention to convert the hydrosilanes into higher boiling chlorosilane species thereby increasing their ease of handling and recovery.